Retroactive memory of a visual discrimination task in the rat: role of temporal-entorhinal cortices and their connections.

It has previously been shown that the temporal and entorhinal cortices may be critically involved in memory. In Experiment 1, rats with either damage to the temporal cortex (TC), lateral entorhinal cortex (LEC), or the medial entorhinal cortex (MEC) were tested for retention of a preoperatively acquired simultaneous brightness discrimination task. TC and LEC lesions impaired retention, whereas MEC lesions were without mnemonic effect. In Experiment 2, rats with either disruptions of the anterior neural connections of TC (TC/Ant), posterior connections of TC (TC/Post), or conjoint disruptions (Ant/Post) were tested for retention of the visual discrimination task. TC/Ant and Post/Ant lesions resulted in relatively mild, but significant memory impairment, whereas a profound effect was seen after TC/Post lesions. The results are discussed in terms of a very important role for LEC and its connections with TC in mnemonic function.